1. Field of the Invention
The present invention relates to a radiation source for use in endovascular radiation treatment with fission product radioactivity and/or irradiation activated radioactivity, which radiation source is provided in the form of a wire and is suitable for being delivered in a catheter to the selected site to be treated within the vascular system of a patient. The invention further relates to use of said radiation source as well as a method of treatment.
Endovascular radiation treatment is the present method of choice to prevent formation of scar tissue in a blood vessel which has been injured in various ways, for example, as trauma from surgical or diagnostic procedures or for treatment of cancer and tumours. One area of the vascular system of particular concern with respect to such injury relates to coronary arteries that are subjected to procedures for removing or reducing blockages due to plaque within the arteries. Partial and even complete blockage of the coronary arteries by the formation of an arteriosclerotic plaque is well known and a serious medical problem. Such blockages may be treated using arterectomy devices which mechanically remove the plaque, hot or cold lasers which vaporise the plaque, stents which hold the artery open and other devices and procedures well known in the art. The most common of them is the percutaneous transluminal coronary angioplasty (PTCA), more commonly referred to as balloon angio-plasty.
2. Description of the Related Art
Long term success of balloon angioplasty procedures is largely limited due to restenosis or re-closing of the intraluminal passageway through the artery by formation of scar tissue. Restenosis is experienced in approximately 30 to 50% of the patients within six months after balloon angioplasty. Apparently, restenosis is to a significant extent a natural healing response to the vessel injury caused by inflation of the angioplasty balloon.
Prior attempts to inhibit restenosis have included the use of various light therapies, chemotherapeutical agents, stents, arterectomy devices, hot and cold lasers and so on. The most promising approach to inhibit restenosis after PTCA is the use of endovascular radiation therapy, i.e. the exposure of the potential or actual restenotic site to ionising or radioactive radiation (brachytherapy).
Another important field for radiation treatment is the localised, internal radiation treatment of cancer, tumours and/or non-malignant cell growth. The advantage of a localised radiation treatment is that the healthy tissue surrounding said tumour is exposed to the possibly hazardous radiation to only a very minor extent, since the radiation can be directed specifically to the target region of the tumour.
Although endovascular radiation therapy in general has been applied advantageously, the devices available for delivery of radiation sources and the radiation sources themselves have certain drawbacks which limit their usefulness. Typically, the devices include a catheter, which is directed by way of a guide wire inserted therein to the site of treatment. The catheter is then used to internally direct the radiation source to the site of treatment.
One typical problem encountered with the catheter and/or the radiation source is related to stiffness of the source which is essentially proportional to its length. Thus shorter radiation sources are typically used to allow them to follow the tortuous anatomy of the heart. To irradiate the entire site of the vessel to be treated a so-called xe2x80x9cstepping-treatmentxe2x80x9d is then employed, wherein the radiation source is moved back and forth in the vessel. Since, however, exact positioning is not possible in a constantly moving vessel, irradiation is not precisely controllable in this xe2x80x9cstepping-treatmentxe2x80x9d. Thus, long sources are desirable which allow for one-step treatment of the site in its entire length.
For example, U.S. Pat. No. 5,833,593 discloses a flexible source wire which is modified at its treatment end to receive a radioactive element. A plug seals the unmodified section of the source from the lumen of the modified segment or container which contains the radioactive element. Both ends of the source wire are sealed to prevent leakage of radioactivity.
U.S. Pat. No. 5,683,345 discloses an apparatus and a method for brachytherapy. The radiation source used according this document consists of individual treating elements which may be joined together to form a train of treating elements by use of several lengths of high tempered spring wire to prevent the treating elements from becoming too spaced apart while moving through the catheter.
Other typical drawbacks encountered with prior art radiation sources and devices for delivering the same to the site to be treated are related to the duration of exposure, controllability of the radiation exposure (dosage, homogeneity of treatment), the necessity to conduct a xe2x80x9cstepping-treatmentxe2x80x9d, or difficulties in completely and controllably retracting the radiation source from the catheter and therefore the risk of undesirable exposure of both the patient and any medical personal xe2x80x9chandlingxe2x80x9d the treatment device.
To solve this problem the European patent application No. 99 111 100.6 discloses a radiation source comprising a deflectable container comprising at least two seeds or radiation emitting elements. The deflectable container joins the relatively short and stiff seeds to form a flexible radiation source. Similarly EP 99 111 099.0 teaches to form a flexible radiation source by directly linking the individual seeds together while still allowing relative movement. Still both radiation sources have the problem that they are limited with respect to miniaturisation in that they either require the container or require providing the linkage between the seeds. The latter radiation source further implies the risk that the linkage between the seeds is interrupted during the treatment. In this case it may be difficult to retract the entire radiation source out of the body to be treated.
Further, in manufacture of the seeds or source there is the constant demand for miniaturisation, since only miniaturisation will provide sufficiently small sources to treat smaller vessels of the patient and thus to successfully allow for cancer or tumour therapy in other anatomical sites.
It is the object of the invention to overcome these and other drawbacks of prior art radiation sources.
According to the present invention there is provided a radioactive radiation source in form of a wire comprising a matrix of a ductile and/or plastic binder material and a radioactive and/or activatable material.
Preferably, the plastic binder material has a low capture cross-section for the method of activation of the activatable material and/or a low attenuation factor for the emitted radiation. More preferably the ductile and/or plastic binder material is of non-ceramic nature and comprises a metal, a metal alloy or mixtures thereof or a radiation resistant plastic material, preferably a synthetic rubber.
Preferably, the radioactive or then xe2x80x9cactivatedxe2x80x9d material is selected from xcex2-emitters, xcex3-emitters and/or x-ray emitting materials. More preferably the radioactive material is a nuclear fission product or is an activatable material activated by nuclear excitation by particles, preferably neutrons, protons or photons. Most preferably the material has a maximum particle energy of xcex2-radiation of at least 500 keV, or a photon energy of xcex3- and/or x-ray radiation in the range of 20 to 100 keV. In a preferred embodiment this radioactive and/or activated material is selected from Sr/Y-90, Tm-170, Si/P-32, P-32, Cl-36, Zn-123, Ce-144, Tb-160,Ta-182, Tl-204, W/Rh-188, Ir-192 and Se-75 or mixtures thereof.
The radioactive and/or activatable material is preferably used in elemental form and/or in form of a compound insoluble under the prevailing compositions, preferably in form of an oxide, fluoride, titanate, carbonate, cermet or ceramic.
The radiation source of the present invention generally has a ratio of length to diameter of xe2x89xa72:1, a length in the range of less than 1 to 25 mm and a diameter in the range of 0.01 to 1 mm.
The radiation source of the invention may further comprise a means for containment which is preferably a capsule or a coating.
The radiation source of the invention can be used for radiation treatment of a mammal, preferably a human being. Preferably the radiation source of the invention is used in brachytherapy, preferably endovascular brachytherapy, to treat restenosis, cancer, tumours and non-malignant cell growth or scar tissues.
The present invention makes possible the objects of (1) providing a radiation source having increased mechanical stability at sufficient flexibility of the source to follow the bends of a small vessel, of (2) providing improved security in view of leakage of radioactive material in case the source is damaged or otherwise manipulated during manufacture thereof e.g. by cutting or forming the same, of (3) providing a considerable simplification in manufacture of producing the radiation source, especially when activatable materials are used, and of (4) allowing for miniaturisation of the source in the sub-millimeter region.